Preventing coke formation in pyrolysis of ketones



J. E. MolsE' Filed Jan. 13, 1948 PREVENTING COKE FORMATION IN PYROLYSIS 0F KETONES meant/11% 0750,

2 d pv dmadomn mmU Z dl r Jan. 9, 1951 r o b n e v a Q Clbbor'rzeg James E. mouse Patented Jan. 9, 1951 PREVENTING COKE FORMATION IN PYROLYSIS OF KETONES James E. Moise, Baton Rouge, La., assignor to Standard Oil Development Company, a corporation of Delaware Application January 13, 1948, Serial No. 2,016

This invention is directed to a process for treating apparatus for carrying out reactions, such as are used in the production of gases and vapors by the distillation and cracking of materials containing them, in the vapor or liquid phase in metal wall reaction chambers or in the presence of metal parts or elements. larly this invention relates to the conditioning of alloy steels containing high percentages of chromium and nickel which are to be used in the distillation and cracking of materials in the vapor or liquid phase.

In commercial processes in which organic compounds are distilled or cracked in tubes, vats, chambers or containers composed of ferrous alloys containing high percentages of chromium and nickel, it is a well-known fact that the high nickel content of the reaction chamber surfaces results in the formation of excessive amounts of coke which soon fills the tubes, vats, chambers or the like, necessitating costly shutdowns for purposes of cleaning out the coke.

It is therefore the main object of this invention to provide a method for conditioning the surfaces of a high chrome-high nickel steel prior to its use in the cracking of organic compounds so as to substantially reduce or even to eliminate coke formation.

According to the present invention the above difliculties due to coking can be overcome by pretreating the metal alloy with certain gases such as carbon monoxide or mixtures of carbon monoxide and hydrogen. The invention contemplates the practice of reaction processes of the character referred to, by preliminarily giving this gas treatment to the metal surface or to the-interior surface of the metal piping, vat, chamber or container which is to be employed in the reaction process so as to condition the metal surface and thereby prevent excessive coking when the metal surface is subsequently used in the above-dc scribed process.

The invention will be described in connection with the process of cracking ketenizable material such as acetone, acetic acid, acetic anhydride or the like to produce ketene, but this is intended to illustrate the method and the invention is not intended to be limited to such use. In general all the prior art processes either definitely state, or by setting forth examples, indicate that the pyrolysis of acetone or other ketenizable material should be carried out in carbon. copper, quartz or silver pyrolysis apparatus. While copper is satisfactory because of its non-catalytic activity with respect to ketene, from the struc- More particu- 7 Claims. (Cl. 260-5855) tural standpoint and for high temperatures use, copper presents certain disadvantages. For example, it may become necessary to sheathe or otherwise protect the copper reaction chamber in order to prolong its life. Furthermore, copper oxidizes during periods of regeneration and is not structurally strong. A high chrome-no nickel steel fails upon repeated heating and cooling, unless tempered by slowly heating or cooling each time. This is impractical in an emergency shutdown, for example, when the temperatures have to be dropped rapidly. Carbon steel is unsatisfactory because it causes severe coking and is not capable of withstanding temperatures over 1100 F. l A high chrome-low nickel steel such Chromium 23-27% Nickel 12-20% Carbon less than 0.2% Substantially iron Balance Such a material has the advantage over copper in that it is not oxidized at operating temperatures and it has the advantage over silver in costs. Yields may be obtained that are as good as any obtained by using copper or silver.

For better appreciation of the invention, reference is made to the accompanying drawing in which numeral 2 represents a vaporizer means for acetone, which may be a simple coil as shown,

or a metal stillpot or the like. The vaporizer is connected by line 3 to preheater 4 which likewise may be of simple construction, comprising merely an S-coil or the like.

The preheater is illustrated as a coil of large diameter to provide low pressure drop and may be composed of the alloy described above. However, it may, if desired, consist of rows of straight tubes connected in series or parallel by means of return bends or headers. It is connected by conduit 5 to pyrolysis chamber 5 which may be a single tube or coil or other type of enclosed chamber, but is of less diameter than the preheater and is composed of the alloy described above. Chamber 6 is connected by line I to absorption tower 8 which may be of any convenient construction.

Tower 8 is provided with conduit means 9 for introducing acetic acid to be reacted with the ketene and with draw-oft" means 19 at the base of the column connected with fractionator H. The upper part of the absorber i provided with vapor take-oil means i2 connecting with condenser l3. Fractionator I! is provided with bottom draw-off means It and vapor take-off conduit l5 which passes through condenser i6 to the top of absorber 8. Part of the condensate from condenser I6 is returned to fractionator it through line 15A for reflux and at least apart is preferably passed to absorber 8 through line 25'. Condenser I3 is connected with line H to scrubber [8 which is provided at its top with means 9 for introducing scrubbing liquid and vent line 20 for removing gases and connects at its bottom with line 9 into the absorber 8; The liquid condensed by condenser If. is recycled by line 23 back to the feed inlet to the vaporizer and preheater zones. Means are provided in absorber 8 and fractionator H' for supplying heat, such as steam coils 2| and 22.

In operating the processor this invention, a positive gage pressure of about five pounds is maintained on the apparatus butwith an inlet temperature of the gas to the cracking zone of about 1159 to 1200 F. andan outlet temperature for the vapors of about 1300 52-1400 F. when acetone is being cracked. The contact time of vapors with cracking temperatures should preferablybe between 0.25'and'0f75 seconds, and the'vapors preierablyshould'have amass velocity in. the cracking zone of about 10-40 lbs./ sq. it./sec.

One method of employing the conditioning processof this invention'might consist in setting upapparatus as shown'in'the'drawing and then introducing at the inletiv end the gases required for? the process, heating them by furnace operationizand' by proper controls, placing the gases under the desired temperature and'pressure'conditions;andletting them circulate throughout'tlie channels through which the=ketenizable material will. circulate in the cracking system and permitting this treatment to continue for the period necessary to induce the'desired conditions; and then evacuating the entire system of the gases after which the system will be ready for the preparation of ketene by'the crackingof ketenizable .material.

Inconnection with the: process of cracking organic compounds inapparatus, the surfaces of 'which. are composed of high chromium-high nickel steel, this invention therefore contemplates as'a preliminary step the introduction into the closed vessel of a gas such as carbon monoxide or a' mixture of carbon monoxide and hydrogen in the ratio of 111-211 Hz/CO under a temperature; of about 1200 F. and'a pressure of about U-lOOp; s. i. g;, preferably about 5p. s. i. g. for a period of 1-24 hours. While temperatures of 1200TK are ordinarily sufficient, temperatures of upfto 1809" may be used if-desired.

The natureand objects or the present invention having thus been fully described and illustrated, what is claimed as new and useful and is desired to be secured by Letters Patent is:

1. In a process in which a ketene is produced by pyrolysis of a dialkyl ketone in a ferrous metal container, the inside surface of which is composed of aferrousmetal alloy containing23-27% chromium, and 12-20% of nickel, whereby there results an excessive coke formation, the method of preventing said excessive coke formation which consists in preliminarily contacting said inside surface with carbon monoxide at a temperature of 1200-l590 F.

2. In a process for the manufacture of ketene by the pyrolysis of a dialkyl ketone wherein a chemical reaction in a ferrous metal container, the'inside surface of which is composed of a ferrous metal alloy containing 23-27 chromium, 12-29% nickel and less than 0.2% carbon, results in excessive coke formation on the inner surface of the container, the method of preventing said excessive coke formation which consists in preliminarily contacting said inside surfaces with a gas containing carbon monoxide at a temperature of about 1200 F.

3. Process according toclairn 2 in which dialkyl ketone is acetone.

4. Process according to claim 3 in which the inside surface is contacted with a. mixture of carbon monoxide and hydrogen.

5. In a process for the manufacture of ketene by the pyrolysis of a dialkyl ketone. wherein the pyrolysis is carried out in a closed metal reactor composed of a ferrous metal alloy containing 23-27% chromium, 12-20% nickel and less than 9.2% carbon to which heat is supplied bytrans fer through the metal walls of the reactor, whereby there' results an excessive cokeformation, a method of preventing'said excessivecoke formation which consists of a preliminary treatment of the inside surfaces of thereactor walls with. a gas containing substantial. quantities of carbon monoxideat temperatures of about 1200 F.

6. Process according to claim 5 in which the dialkyl ketone. is acetone.

7. Process according to claim 6' in which the inside surface is contacted with a mixture of hydrogen and carbon monoxide inzthe ratio of 1 t 1 to'2':1.

JAMES E. MOISE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,872,91 Dreyfus Aug. 23, 1932 1,941,271 Pollock Dec. 26, 1933 2,069,243 Graves et al Feb. 2, 1937 2,215,950 Young Sept. 24, 1940 2,218,966 Boese Oct. 15, 1940 2,393,778 Hull Jan. 29, 1946 

1. IN A PROCESS IN WHICH A KETENE IS PRODUCED BY PYROLYSIS OF A DIALKYL KETONE IN A FERROUS METAL CONTAINER, THE INSIDE SURFACE OF WHICH IS COMPOSED OF A FERROUS METAL ALLOY CONTAINING 23-27% CHROMIUM, AND 12-20% OF NICKEL, WHEREBY THERE RESULTS AND EXCESSIVE COKE FROM FORMATION, THE METHOD OF PREVENTING SAID EXCESSIVE COKE FORMATION WHICH 